Radiofrequency transformer



May 12, 1925. 1,537,224

S. COHEN RADIO FREQUENCY TRANSFORMER FiledUafi. 27, 1923 Hr MM I'I M P;BY M34. (55721 K; A TTORNE Y.

Patented May 12, 1925 UNITED STATES SAMUEL COHEN, O'F BROOKLYN, NEWYORK.

RADIOFREQUENCY TRANSFORMER.

Application filed January 27, 1923. Serial No. 615,210.

To all whom it may concern:

.Be it known that I, SAMUEL CoHEN, .a citizen of the United States,residing in Brooklyn, county of Kings and State of New York, haveinvented certain new and useful Improvements in R-adiofrequencyTransformers, of which the following is a specification.

My invention relates to transformers for utilization in connection withcircuits traversed by high frequency currents, and particularly currentsof radio frequency, as utilized in radio telegraph, telephone or othersystems.

In accordance with my invention, the transformer structure is of generalapplication, but is particularly utilizable as an inter-valvetransformer, as for coupling the anode circuit of a thermionic device,as of the audion type, with the grid or control electrode circuit of asucceeding stage of an amIplifying system.

n accordance with my invention, the width or thickness, or axial length,of the transformer coils is small, and preferably very small as comparedwith the diameter of the coil, this relation effecting high inductanceand low distributed capacity, both of which are desiderata intransformers of this type.

In accordance with my invention, the primary and secondary coils arewound upon suitable supports or forms, in suitably close relation toeach other, side by side, the material of the support or form being suchas has'low dielectric constant, and further to reduce capacity effectsthe form or support is suitably cut away, skeletonized or otherwisereduced as to the total mass of form or support material present inassociation with the coils, and preferably adjacent them or betweenthem.

My invention resides in a transformer of the character hereinafterdescribed and claimed.

For an illustration of one of the various forms my invention may take,reference may be had to the accompanying drawing, in which:

Fig. 1 is a top plan view of structure embodying my invention.

Figs. 2 and 3 are sectional views, partially in elevation, taken on thelines 22 and 3-3, respectively, of Fig. 1.

Fig. 4 is a side elevational view of the winding support or form.

Fig. 5 is a sectional view of the same.

Fig. 6 is a side elevational view of the form with the windings woundthereon.

Fig. 7 is an end elevation of the form with the windings thereon.

Fig. 8 is a diagrammatic View illustrating one of the various uses of myinvention.

Referring first to Fig. 8, P is the primary of a radio frequencytransformer connected in the anode circuit of a thermionic amplifier orsimilar device V, comprising the filament or cathode f, grid 9 and anodeor plate a. The coil L, which may be the secondary of a couplingtransformer, or a coil itself directly absorbing electro-radiant energyfrom the natural media, is shunted by a tuning condenser C, and the gridg and filament f of the amplifier V are connected to opposite terminalsof the coil L and condenser C, as well understood in the radio art. Thefilament f is heated to incandescence by current from the battery Acontrolled by therheostat r. In the circuit of the anode a, in additionto the aforesaid primaryP, is the source of current or battery B. Thecurrents of high or radio frequency impressed upon the grid circuit ofthe tube V are amplified thereby and appear in greater amplitude in theprimary P, which inductively affects the secondary coils S and Scumulatively affected by the primary P and aiding theirelectromot1veforces in influencing the potential of the grid 7 of thesecond thermionic device V which may be an amplifier, as shown, or maybe a detector or other type of device.

My invention relates to the transformer comprising the primary P and oneor more of the secondary coils S, S

It is desirable for best operation that the inductance of the primaryand secondary coils be high, and that nevertheless their capacities, asdistributed capacities, shall be low. To this end, the coils are madeaxially short, narrow, or thin, and of a diameter which is greatcompared with the width or thickness.

For this purpose there is provided a form or support F, Figs. 2 to 7inclusive, of fibre,

ebonite, hard rubber or other suitable material, preferably a materialwhose dielectr1c constant is low or sufliciently low for the purposesinvolved.

The form is provided with a circumferential groove or slot p, in whichis wound the primary coil P, as indicated in Fig. 7. Adjacent the.groove or slot 12 is a circumferentially extending groove or slot 8, inwhich is wound the secondary coil '8. \Vhere suitable or desired, thesecondary winding as a Whole may be divided into two parts S and S asindicated in Fig. 8. In such case the form F may be provided with athird slot or circumferential groove 8 in which is wound the secondarycoil S as indicated in Fig. 7.

It will accordingly be noted that the width or thickness of each of thecoils is very small as compared with the diameter, this generalproportion effecting high inductance and low distributed capacity.- Byway of example, it may be stated that the primary coil P may consist of131 turns of No. 40 enamelled copper wire, while each of the coils S andS consists of 100 turns of No. 40 enamelled copper wire, whereby thetotal of the secondary turns is 200. Each of the slots p, s and s isapproximately .032 inch in width, and the internal diameter of each ofthe slots, and therefore of each of the coils P, S and S isapproximately 3 of an inch.

Further to reduce the distributed capacity, the mass or amount of thematerial of the form F is reduced. This, in the example illustrated, isaccomplished by boring through the form F the holes H, suitably spacedcircumferentially of the form F in suitable number and size, andpreferably forming reductions of material adjacent the windings or coilsthemselves, as indicated in Fig. 6. In other words, the holes Hintersect the winding slots 10, s and 5 The material of the form F maybe otherwise suitably reduced, particularly adjacent the actual windingsthemselves.

Conveniently to bring out the ends or terminals of the primary andsecondary windings, there may be provided the transversely extendingslots 1), suitably spaced from each other circumferentially of the formF in a number suitable for bringing out the number of coil ends orterminals involved.

While I have indicated the transformer as comprising a single primaryand two secondary coils, it will be understood that there may beemployed more than one primary coil and either one secondary coil or anygreater number.

The example above given is for a radio frequency transformer: suitablefor intervalve or inter-amplifier use in connection with wave lengthsranging from about 175 to 650 meters;

The same general features and ideas of construction may be utilized,however, for longer wave lengths.

In the' example illustrated in connection with the aforesaid shorterwave lengths, the inductance of the primary P may range from about .52to about 1.2 milli-henrys,

while the inductance of the secondary may range from about .875 to 2.2milli-henrys, these values varying within the ranges indicated forvariations of inter-electro capacity within the valves or audionsthemselves. Furthermore, in accordance with the examples of dimensionsand structure above given, the distributed capacity of the transformercoils is low and within a range from about .5 to about 1.5micro-microfarads.

Features of my invention are also utilizable in connection with audiofrequency transformers, in which case the inductance of each of thewindings of the transformer may be of the order of henry with adistributed capacity of the order of 2 micromicrofarads.

The winding unit as indicated in Fig. 7 having been completed, it may besuitably mounted or housed, as by recourse to structure as follows: ahousing or hollow member D of insulating material, preferably moldedmaterial, as condensite, bakelite or the like, has a chamber E in whichthe form or support F, carrying the windings, is placed, as indicated inFigs. 2 and 3, in such position that the coil ends or terminalsextending through the different slots 5 are suitably positioned forconnection with particular binding posts intended therefor. Thus, theform F is placed in such position in the cavity E that the differentslots 6 come opposite or adjacent the proper ones of the four bindingposts, I, J, K and M.

These binding posts comprise screws 0 extending upwardly through themember D from the recesses N, through the washers d. Threaded upon eachscrew is a locking washer or nut e, between which and the finger nut 71,threaded upon the screw, may be held and bound a circuit connection orconductor.

After placing the form F in the position indicated in Figs. 2 and 8, themetallic holding strips or lugs i are placed in position and the screws0 passed therethrough and the member D as aforesaid, the screws 0 whentightened holding the lugs z snugly and firmly in position and therebyholding the form F in desired position. To these lugs 2' may beconnected the aforesaid ends or terminals of the windings or coils P, Sand S thereby effecting electrical communication with their respectivebinding posts.

Thereafter the chamber 1 and the recesses N may be filled with molteninsulating material which on cooling solidifies. For example, paraffineand beeswax may be employed, or any other suitable or equivalentmaterial, the same being indicated at 9'. \Vhen the transformer is to beutilized for short waves, as, for example, those ranging from about 175to about 650 meters, it is preferred that no material be introduced orused, since its close approach to the windings will tend to increase toundesired extent the distributed capacity of the windings. However, forthe longer wave lengths material may be used, but even in the case ofthe l onger wave lengths it may be omitted.

In the member D are molded the interiorly threaded metallic inserts k,into which are threaded the screws m to hold in place the bottom plate nhaving the integral lugs or cars 0 having holes 9 to accommodate screwsfor holding the structure to any suitable base or support.

It will be noted concerning the construction hereinbefore described thatthere is no metallic or conducting part disposed in or close to thefields of the transformer windings. It is desirable to avoid thepresence of metallic or conducting material in the fields in order toprevent an increase of the apparent resistance of the coils or circuits,such increase of resistance increasing the losses, which should be keptas low as possible.

What I claim is:

l. Transformer structure of the character described, comprising ahousing of insulating material having a chamber, a transformer unitdisposed in said chamber and comprising a plurality of grooves andwindings in said grooves, conducting members projecting from oppositesides of said chamber over said unit within said housing, connectionsfrom said coils to said conducting members, and binding posts extendingthrough said conducting members to the exterior of said housing.

2. Transformer structure of the character described, comprising ahousing of insulating material having a chamber, a transformer unitdisposed in said chamber and comprising a plurality of grooves andwindings constituting a pair of secondary coils and an intermediateprimary coil in said grooves, conducting members projecting fromopposite sides of said chamber over said unit within said housing,connections from said coils to said conducting members, and bindingposts extending through said conducting members to the exterior of saidhousing.

In testimony whereof I have hereunto affixed my signature this 22d ofJanuary,

SAMUEL COHEN.

